# Simple filter circuit: Phase shift

by 600burger
Tags: circuit, filter, phase, shift, simple
 Mentor P: 40,717 Simple filter circuit: Phase shift Yes, split the T(s) up into its magnitude and phase components (you know the trick of multiplying by the complex conjugate of the denominator?), and then plot them on your frequency graph (log frequency on the horizontal, and linear dB and phase on the vertical). The reason that your prof said to set w0 = 1/RC is that for a single-pole lowpass filter like this T(s), you will get the flat 0dB gain line from low frequencies that tips over and starts down at -20dB/decade. The frequency it tips over and starts down is called w0, and is defined as the half-power point for the T(s). Since T(s) is a voltage transfer function as you have written it, you get half power when the voltage is down by a factor of $$\frac{1}{\sqrt{2}}$$
 Quote by berkeman The reason that your prof said to set w0 = 1/RC is that for a single-pole lowpass filter like this T(s), you will get the flat 0dB gain line from low frequencies that tips over and starts down at -20dB/decade. The frequency it tips over and starts down is called w0, and is defined as the half-power point for the T(s). Since T(s) is a voltage transfer function as you have written it, you get half power when the voltage is down by a factor of $$\frac{1}{\sqrt{2}}$$